This invention relates to the field of wheel suspensions, and particularly to wheel suspension systems that independently support the wheels of a trailer, semi-trailer or other vehicle in which a wide and low cargo floor is desired. This invention is an improvement to the wheel suspension system described in U.S. Pat. No. 4,934,733, issued on Jun. 19, 1990, and U.S. Pat. No. 5,016,912, issued on May 21, 1991, both of which are assigned to the assignee of this invention.
For a variety of reasons, it is desirable to have the cargo floor of a trailer, van or the like as low as reasonably possible. The provision of the low floor provides for more efficient transportation of cargo since the vehicle has a higher load capacity for a given exterior dimension. Easier access to the floor is also obtained when it is placed close to the road surface. These and other advantages of a low cargo floor have motivated the prior art to provide low vehicle floors, although many designs heretofore have not been practical for heavy loads or long-term use.
In U.S. Pat. No. 4,032,167 issued to Chereda on Jun. 28, 1977, there is disclosed a trailer for transporting motorcycles. The Chereda trailer includes a rigid, horizontal frame upon which is mounted a pair of opposed wheels. The two wheels are secured to fixed spindles bolted to the frame. No provision is made for suspending the wheels other than by this rigid attachment, and the Chereda trailer would therefore suffer from the disadvantages of the rigid mounting of the wheels to the load-carrying frame. Devices such as the Chereda trailer have been suitable for light-load applications, but are not practical for heavy use since the rigid attachment of the wheels to the trailer frame causes considerable forces to be transmitted to the frame.
A vehicle suspension is described in U.S. Pat. No. 4,718,692 issued to Raidel on Jan. 12, 1988, in which pairs of pivoting arms support a through axle that extends the width of the vehicle below the vehicle frame. Many such pivoting arm suspensions, as in the Raidel system, have been found applicable to heavy use when incorporating a through axle. See, for example, U.S. Pat. Nos. 3,140,880 to Masser; 3,704,898 to Schmidt; 3,884,502 to Wagner; 4,166,640 to Van Denberg; 4,202,564 to Strader; 4,252,340 to Egging; 4,427,213 to Raidel, Jr.; 4,465,298 to Raidel, Sr.; 4,541,653 to Raidel; 4,580,798 to Roelofs; 4,593,930 to Davis; and 4,615,539 to Pierce.
Some suspension systems dispense with the through axle and provide independent support for each wheel through a pivoting arm. For example, in British patent specification 692,854 to Waters, published on Jun. 17, 1953, a vehicle suspension system is described in which each wheel is carried by a radius arm which is pivotably connected to the vehicle chassis. This pivoting arm concept has been employed in prior devices of varying sophistication. See, for example, U.S. Pat. Nos. 2,507,980 to Knapp; 3,078,104 to Chalmers; 3,356,386 to Taylor; 4,619,578 to Routledge; and 4,666,181 to Wegner. Absent the through axle, however, the pivoting arm devices of the prior art have not been designed to provide adequate strength and stability, particularly in terms of the lateral forces transmitted to the suspension upon turning of the vehicle. Moreover, many of these devices require a good deal of space for the components, which space can be better used for transporting cargo.
There continues to be a need, therefore, for a vehicle suspension apparatus which will permit the floor of the vehicle body to be closer to the road surface. It has further remained desirable to have as compact a suspension as possible to maximize efficient and convenient use of vehicle space and to be substantially flat along the length of the trailer through the wheel region of the trailer.